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Wordie Creek Formation
Geologic formation in Greenland From Wikipedia, the free encyclopedia
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The Wordie Creek Formation is an uppermost Permian and Lower Triassic geologic formation in Greenland, outcrops of which are located in Northeast Greenland National Park (until 2008 Tunu County, Danish: Østgrønland, English: East Greenland). In 2017, it was suggested to be raised to group status, as the Wordie Creek Group.[1]
The Lower Triassic sediments in the region were discovered in 1926 independently by James Wordie and Lauge Koch, and the latter named the formation.[1] The rock layers preserve fossils of invertebrates (e.g., ammonoids,[2] gastropods[1]), fishes (coelacanths, ray-finned fish, cartilaginous fish)[3][4] and temnospondyl amphibians,[5][6] dating back to the Induan age.[7]
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Geology
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Following Surlyk et al.,[1] the Wordie Creek Group is subdivided into two formations, the Kap Stosch Formation and the overlying Godthåb Golf Formation. The Kap Stosch Formation was deposited in relatively deep, partly isolated turbiditic basin, and the Godthåb Golf Formation under relatively shallow marine conditions.
In 1935, Eigil Nielsen[8] recognized five fossil-bearing horizons ("fish zones 1–5")[9][10] corresponding to three ammonoid zones (in ascending order):
- Otoceras zone ("fish zones 1 and 2")
- Vishnuites zone ("fish zones 3 and 4")
- Proptychites zone ("fish zone 5")
The first two ammonoid zones are Griesbachian in age and the last one is Dienerian in age (Induan). The Kap Stosch Formation corresponds to these three zones. A sixth fossiliferous layer, the "Stegocephalian horizon", is present above, which belongs to the Godthåb Golf Formation (Dienerian). The Hypophiceras triviale ammonoid zone below Nielsen's "fish zones" is dated late Changhsingian.[1]
The Kap Stosch Formation is subdivided into the following eight members (in ascending order):[1]
- Nebalopok Member (upper Changhsingian–lower Griesbachian)
- Immaqa Member (lower Griesbachian)
- Fiskeplateau Member (lower Griesbachian)
- Knolden Member (lower Griesbachian)
- Pyramiden Member (lower–upper Griesbachian)
- Naasut Member (upper Griesbachian)
- Falkeryg Member (lower Dienerian)
- Vestplateau Member (lower Dienerian)
The Godthåb Golf Formation is not subdivided into members.[1]
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Paleobiota
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A diverse vertebrate fauna composed of temnospondyl amphibians and fishes is known from the formation.[3][5][11] Fossil fishes are also known from the Permian Ravnefjeld Formation ("Posidonomya shale") of Greenland.[8]
Amphibians
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Notes Uncertain or tentative taxa are in small text; |
Fish
Lobe-finned
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Notes Uncertain or tentative taxa are in small text; |
Ray-finned
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Notes Uncertain or tentative taxa are in small text; |
Cartilaginous
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Notes Uncertain or tentative taxa are in small text; |
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References
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